1. Field of the Invention
The invention is based on an electrical resistance element. The invention also relates to the use of such a resistance element in a current limiter.
2. Discussion of Background
A resistance element of the type mentioned at the beginning is known from EP 0 363 746 A1 and from the paper by T. Hansson "Polyathylen-Stromwachter fur den Kurzschlu.beta.schutz" [Polyethylene current relay for short-circuit protection], published in ABB Technik 4/92 (1992), pp. 35-38. This resistance element comprises a thin plastic plate of filler-containing polyethylene, which is arranged between two comparatively thick electrodes. At room temperature, this resistance element has a very low resistance and can then carry the nominal current flowing in a low-voltage distribution network without any problem. For several seconds, the resistance element can also readily carry a nominal current several times higher, since the comparatively thick electrodes can temporarily absorb the Joulean heat generated in the resistance element. If, on the other hand, a short-circuit current occurs, the temperature of the resistance element increases very rapidly in a very thin surface layer at the electrodes, preferably consisting of silver-plated copper, and melts the polyethylene located in this layer. As a result, the resistance of the resistance element increases abruptly and reaches about 30 times its initial value in less than one millisecond. The short-circuit current is thereby greatly reduced and can be disconnected by a power circuit-breaker of low short-circuit breaking capacity, connected in series with the resistance element.